Note: (1) Each year the quiz was at a different web location and the questions were slightly different.
So the formula would have been different too, introducing a little erraticism into the absolute values.
I believe the percentages are more reliable than the absolute data. And that
the results shown below
where
many people took the 2003 quiz
are comparable.
(2) 1 hectare = 2.47 acres.

Dang. My percentage appears to be increasing.
As these programs are from different web sites each year,
some variation may be differences in what data are collected and what formulae manipulate them.
However, I would expect an increase from 2001 to 2003, as I began to
eat meat (about 3 oz per day).

The worldwide average footprint of 2.4 hectares (6 acres) per person
exceeds the available acreage.
I don't know what that means but it sounds dangerous.
It sounds like
the world is overpopulated

They asked you how much of the biosphere should be set aside for other species.
I said 80%.

Based on my above results, their model said:

Your choice means that you maintain that each person should be able to live a satisfying life
within an average of 0.4 hectares
or 1 acre.

The model said that my 80% and footprint data meant that it required 18.7
Earths to support each member of the present human population
at my standard of living.

My response is:

USA and the rest of the Earth should have a twentieth of the current world population.

I recommend that 19 out of 20 decide to not have children.

I have chosen to be in the non-child-bearing 95%.

It is obvious that the impact of people on the planet increases with population.
But it was in 1998 that Yale economists William D. Nordhaus and Joseph Boyer first
developed a model of the cost of the human population on
future living standards.
They found that:

The lifetime cost of each person's impact on their environment
was then about $100,000 in a high-income country.
It fell with income, reaching $2500 per person in low-income countries.

The Zimmerman Shadow Ecology Footprint

Some friends wanted an "extra deduction for not having kids". Therefore,
as the data start to come in from my friends, I have came up with the
Zimmerman Shadow Ecology Footprint.

This Shadow Footprint is the shadow of additional load that is cast by people with children
(because they are throwing a shadow of increased population into the future)
and by people with larger pets.

While there are many ways to create a different formula, this is the one that I am using:

The estimated "shadow footprint" is the footprint cast by one's offspring
and pets.
The formula is:

pets get divided by
"fudge-factor" because one's mileage to the vet is included in one's own
data,
as is the space to house the pet (except for horses, etc), but cost of
vet's services and facilities,
purchase of protein-rich pet food, environmental
impact of pet poop, etc. are not included.)

What is the "shadowed footprint" (the sum of the basic ecology footprint
plus the ZSEF) for the average USA citizen? It comes to a value of "50-acres" for
this footprint-with-shadow. Here's how.

USA citizens have a fertility of over-replacement, contributing to world population increase.
So the average adult American shadow print is over 24 acres - say 26 acres - for the "kid
component".

Then, given than some people have horses, many have dogs, pot-bellied pigs,
etc., the average shadow print (I am guessing wildly) is say 2 for pets.

So the total is 52 ( = 24 + 26 + 2)

These are not actual acres; they are just for comparison purposes.
And for easy comparison purposes, and given that all of this is very
approximate (as in "smoke and mirrors"?), I am just going to call that "50", as any
economist or statistician might do.

Results in 2003 by others, living in USA except as noted; some data added for 2008 (using
calculator referenced in footnote [1]):

'Transportation' includes
miles driven,
ride sharing, fuel efficiency, use of public transportation,
and air travel.
The average car in the USA is driven (sit down,
wait for it, ...) 17,000 (seventeen thousand) miles annually.

'Housing' includes
size of the home (or for Republicans, homes) you live in,
use of green electricity, and use of energy efficient appliances.

Range in 2003:
"in some countries, the average is as low as 0.5 hectares (1.2 acres), while others
use as much as 13 hectares (32 acres) per person. Even within any given
country, individuals' footprints vary widely."

Try it! Remember that the source of the models and the comparative USA footprint
varies year-to-year.

Fine print:
Your mileage may vary;
there is some rounding in the data.

A comment on 'environmentalists' like Al Gore

Comments by Saul Griffith, an eco-minded engineer, cited by David Owen in his The New Yorker
(May 17, 2010) article "The Inventor's Dilemma: an eco-minded engineer discovers the limits of invention"
[p. 30]:

Griffith told me,
"I know very few environmentalists whose heads aren't firmly up their ass.
They are bold-facedly hypocritical, and I don't think the environmental movement as we know it
is tenable or will survive.
Al Gore has done a huge amount to help this cause, but he is the No. 1 environmental hypocrite.
His house alone uses more energy than an average person uses in all aspects of life, and he flies prodigiously.
I don't think we can buy the argument anymore that you get special dispensation just because what you're
doing is worthwhile."

Griffith includes himself in this condemnation.
He said,
"Right now, the main thing I'm working on is trying to invent my way out of my own hypocrisy."